1. Field of the Invention
The present invention relates to heat exchangers for use in a hot air furnace. More specifically the present invention relates to heat exchangers for use in a gas fired, hot air furnace, said heat exchangers being principally adapted to be fired by a fuel burner and further being adapted to be fired under a suction pressure created by an induction draft blower.
2. Description of the Prior Art
Heat exchangers of the type commonly used for gas fired hot air furnaces are found in many residential and commercial installations. In particular compact furnaces adapted to be used either in the basement or some other small or confined area in the house have long used clamshell type heat exchangers to heat room air being passed over the surface of the exchanger. This room air is then circulated within the area to be heated and simultaneously cold air is removed from the area to be heated and recirculated through the furnace. A series of heat exchangers are provided in each furnace depending upon the size of the space or structure to be heated. It has become an industry practice to provide heat exchangers of a pre-selected capacity so that multiples of the heat exchanger may be provided together in a single furnace to reach the appropriate furnace capacity.
Commercial installations often involve a roof top unit to avoid using valuable floor space for heating and ventilating equipment. The size of commercial units is generally limited by cost and shipping requirements. A series of heat exchangers of a pre-selected capacity are usually provided for each roof top unit so that multiples of the heat exchanger may be used to obtain the desired furnace capacity.
Previous heat exchangers have been constructed from two metal sheets such that a fluid flow path is created when the two sheets are asembled. This type of heat exchanger is known as the clamshell type since it is constructed from two separate sheets, usually of metal. Typically a single burner is used to provide heat to the inlet side of the heat exchanger and the products of combustion are removed from the heat exchanger either using an induction draft blower or by convection.
The furnace industry has developed numerous clamshell heat exchangers, the bulk of which appear to have an efficiency of about 75%, efficiency referring to the portion of heat contained in the fuel transferred to the air passing over the heat exchanger. These previous heat exchangers have had various forms including a serpentine form as disclosed in Raleigh, U.S. Pat. No. 3,661,140, a "lamb chop" arrangement as disclosed in Block et al., U.S. Pat. No. 3,140,706, a curvilinear heat exchanger as disclosed in Norris, U.S. Pat. No. 3,294,082, and the other prior art disclosed therein. Other types of heat exchanger configurations can be found in Wilhoite et al., U.S. Pat. No. 3,111,940; and Jaye et al., U.S. Pat. No. 2,808,047; Hollingsworth, U.S. Pat. No. 3,073,296; Peoples et al., U.S. Pat. No. 3,084,682; Reznor, U.S. Pat. No. 3,241,609; Rutherford, U.S. Pat. No. 3,527,292; and Brown, U.S. Pat. No. 1,931,247.
Since the advent of the natural gas shortage of the winter of 1976-1977 and the general awareness of the lack of unlimited natural gas supplies especially the lack of unlimited amounts of natural gas for residential usage and more particularly since many major utilities have now limited new installations of natural gas consuming appliances it has been deemed desirable to develop a highly efficient heat exchanger both for use in a compact residential furnace and for commercial furnace purposes. To resolve the problem of finding a highly efficient heat exchanger the hereinafter described configuration was invented. This new induced draft clamshell type heat exchanger has experimentally been found to be 84% efficient as compared to the 75% efficiency industry produced heat exchanger presently in use.